Factory Block Oil Passage Drilling

[nm9stheham]

Just FWIW..... this question came up in another thread... .how the factory drilled the oil galleries. We looked closely at our 340 block and the galleries look to have been drilled from both ends, AND the drilling diameter steps down ever so slightly every 2" or so, perhaps 1/64th inch per step.

And the oil passages from the galleries to the main webs are the same, with it stepping down from the web to the gallery. We found this while drilling out for the GJ oiling mods. I assume the stepping just make it easier to avoid the chips jamming up the drill and allows oil to be put in regularly.

This also explains why the oiling holes for the lifters varies in size.

Here is a fuzzy pix looking into the back of the passenger side gallery; you can see one of the steps in the gallery.

 

[rumblefish360]

Hummmmmmm, got me on this one.

Keep detailing this with pictures!

 

[nm9stheham]

The thin shiney ring in the hole is one of the small steps in the drill size. Sorry that it is hard to see. These steps decrease in size at each step, and decrease from each end and in the mains oil passages. Toolmanmike gets the prize here, as he said that step-drilling was how it was done, in this thread:

http://www.forabodiesonly.com/mopar/showthread.php?t=327115&highlight=lifter

This particular gallery has a rough segment near the middle, where it looks like the final drill step was not done in the rough cast gallery for the drilling from the back. It is still >1/2" ID so we did not drill it out; but this explains the unusually small lifter oiling hole in the thread above; it was just not properly finished out inside the gallery. (We found that undrilled segment after all the other drilling and an extensive cleaning of course!)

Based on this, it may be worthwhile to inspect the galleries and all oil passages for completed drilling operations end-to-end for critical racing use.

 

[krazykuda]

I assume the stepping just make it easier to avoid the chips jamming up the drill and allows oil to be put in regularly.

I believe that they step drill because they can't drill it all the way at once in one step and still have any tool life. Plus they need to keep spraying coolant on it while they drill, and once the drill gets so deep, the coolant can't get in there to cool and lubricate the drill bit. Plus, you have to keep the chips from building up...

Every time that they have to stop the operation to change the drill bit, is lost blocks that they could have made, so you want to try to make the tools last as long as possible and get them to be replaced during the regular down time when the shift changes so you don't loose production...

 

[EL5DEMON340]

I think this is why a very well known oil mod is used when your going to rev it over 6,500 rpm. Open the oil pump hole and radius, drill out mains to 9/32 I think. Along with other mods.

 

[nm9stheham]

Yep, we were doing the Guitar Jones oiling mods; the holes to the mains increase to 5/16"; that mod is a fun one. Getting the drill to start from the web end where multiple passages meet up is a trick. We started with a vary narrow angle, small reamer to open up the oil supply hole a bit, then followed up with a very small grinder to open it up to 5/16' deep enough to get past the edge of the cam oiling passage. Then, you could start the drill without it grabbing the edge of cam oiling passage.

But the GJ mods don't discuss the oil galleries per se for complete step drilling end-to-end; so that I why I am suggesting an inspection of them. If you find any unusually small lifter oiling holes, that is a distinct clue to that potential issue.

 

[perfacar]

something to think about, in piping runs, as it gets longer, you step down dia, that maintains pressure. also, volume. oil gallery is like a pipe run.

 

[nm9stheham]

something to think about, in piping runs, as it gets longer, you step down dia, that maintains pressure. also, volume. oil gallery is like a pipe run.

Interesting thinking there..... However, for these oil galleries, it looks to be step drilled from both ends... in other words, starting from the back, it steps down to the middle and then steps larger again from the middle to the front. Done the way on both sides. Looks just like a machining consideration (to me).